The invention relates to extrusion, especially the dies that are used in the extrusion process which essentially comprises charging solid extrudable material, such as rubber, to the heat chamber of an extruder, after which the material is heated to a flowable state and forced from the chamber through the opening in a plate or die which is mounted at the discharge end of the heat chamber. The extrudate falls onto a conveyor which removes the extrudate from the extruder which, typically, has a horizontally disposed hollow barrel with a cylindrical bore as a heat chamber. A rotatable screw is disposed in the bore for forcing the heated material through the die at the discharge end of the barrel.
Extruded products, such as rubber automobile and refrigerator door seals are limited to linear extruded formations. The corners of such door seals are presently formed, by hand. For example, the ends of two seals are mitered and held together in a mold, after which similar rubber material is injected into the mold to contact and join the mitered ends to form the corner desired. Removable inserts are placed in hollow sections of the mitered ends, so that the shapes of the seals will not be distorted during the corner forming process which is complex, time consuming and expensive.
The aforementioned door seals can be molded with curved or square corners, but this process is a batch-type process which is much slower than the continuous extrusion process. Moreover, expensive molds are required in the molding process. Thus, it is quicker and easier and less expensive to use the extrusion process, if at all possible.
The extrusion of bends in rubber automobile hose is well known. This is accomplished by eccentrically positioning in the flow channel through which extrudate flows, the cylindrical core or mandrel which is used to form the hollow bore within the hose. The variation in the thickness of the flow pathways along the mandrel, causes the rubber extrudate or hose to bend in the direction of the narrower pathway, or thinner sidewall produced in the hose. Such a process is suitable for extrudates which have a relatively simple shape that is substantially symmetrical about an axis. The aforementioned door seals generally have a complex geometry or shape, so that their formation is incompatible with the hose making process.
A simple, revolutionary way has been discovered to bend or curve a uniform extrudate without radically distorting the shape of the extrudate.
Briefly stated, the invention is in a method and apparatus for substantially varying the length of the pathways which extrudate flows to opposing extremities of a die opening to produce bending or curvature of the extrudate in the direction of the longer pathway.
It has been found that varying the lengths of the flow pathways, rather than the thickness of the pathways, causes the extrudate to bend without substantially changing its cross sectional shape. Thus, the invention has the advantage of producing a more uniform product which does not have any of its sidewalls weakened by a reduction in thickness.